Ok, so it’s kiddie literature.
The book “Ramona Forever” by Beverly Cleary (it’s part of a Ramona series) includes some passages about a young boy learning to ride his unicycle. It includes a couple of illustrations, one of said young boy falling off and the second of him riding successfully. Riding a unicycle is explained by an uncle thusly:
“It’s like riding a bicycle, but instead of balancing sideways, you have to balance back and forth at the same time.” - pg 15
The book is written primarily for 8 - 12 year old girls, of which I am in possession of one.
She was very excited when she found the unicycling in the book.